This protocol exploits the ability of a renin-inhibitory peptide to reduce AII formation with the goal of assessing the contribution of AII to 1)the control of the renal circulation, 2)the control of adrenal aldosterone release, 3)modulation of the responsiveness of these processes to AII with shifts in sodium intake, and 4)renal sodium handling. Studies during the past year involved a systematic comparison of the responses to the renin inhibitor, enalkiren, and to the ACE inhibitor, captopril.